Oh Tae Shik, rather, Oh Kyeon Shik, who has been preparing to become a detective while working a different job, is a private establishment security guard who earns 880,000 won in Daechi Dong, Gangnam. Thanks to his dream of becoming a detective, he is like a bulldozer who does not know how to give up. He always watched CSI and Detective Columbo's movies, analyzing their traits and building his dream of becoming a great detective. He manages to pass the written test, but he doesn't meet the hearing baseline and fails. Then one day, coincidence happens and a fugitive on the run gets caught by Kyeon Shik when he throws a bottle of water he just bought at the runner. Kyeon Shik becomes a hero thanks to this. He has only one wish and that is to be a detective. The major who doesn't know about him promise him a spot on the team. However, the detective team, who are just about to get their investigative independence, are worried that Kyeon Shik will cause trouble and they finally come up with an idea!